The present invention relates to a transducer which is particularly applicable for use in monitoring the angular position of the butterfly valve of an internal combustion engine for the purpose of providing an electrical signal to be processed by an on-board computer or microprocessor system, and it will be described with particular reference thereto; however, the invention has much broader applications and may be used in various instances where a signal indicative of angular position is to be generated.
In recent years, the automotive industry has been in the process of converting the control system of the standard internal combustion engine to a system which can be controlled by a computer or microprocessor. This type of engine control system monitors various operating conditions of the engine and its appurtenances for assimilation and efficient control of the engine. There has been a substantial demand in the automotive industry for transducers to monitor mechanical and electrical engine conditions to create input signals or data for the on-board computer, microprocessor or other digital processing systems. One parameter which is monitored on an internal combustion engine is the position of the throttle valve associated with the carburetor. As the engine load and speed is to be changed, the angular position of the throttle valve is changed. This valve is hereafter referred to as a butterfly valve. The angular change can be caused by a feedback system, such as a vacuum control system, or by a direct manipulation through the accelerator pedal of the vehicle. Irrespective of the manner in which the butterfly valve is oscillated or pivoted, digital control systems for the internal combustion engine generally require an indication of the angular position of the valve at any given time. In the past this angular position was monitored by a sensor including a fixed housing with an internal resistor. The resistor included a wiper carried on a rotor which was adapted to slide along a conductive disk. Rotating the wiper varied the portion of the resistance of the disk which resulted in the creation of a voltage proportional to the angular position of the rotor. The rotor of the position sensor was driven by an extension on the pivoting shaft of the butterfly valve. Calibration of this sensor could be accomplished by rotating the housing on the carburetor. This type positional sensor sometimes requires an interconnecting linkage or mechanical drive between the shaft of the butterfly valve and the sensor itself. The wear between the wiper of the rotor and the resistance member of the potentiometer reduced the life of the sensor. Also, this constant sliding action caused a certain amount of mechanical inertia resisting movement of the wiper in response to movement of the butterfly valve. Such inertia could result in disproportionate sensing. The drive train would take up slack before a change in signal was indicated by the sensor. Sometimes, the sensor would fail due to a heat deterioration. All of these difficulties rendered existing sensors for indicating the angular position of a butterfly valve in a carburetor less trouble free than desired or demanded.
As will become apparent, the present invention relates to a transducer using a linear Hall Effect device for creating a signal proportional to the angular position of a member, such as the butterfly valve of an internal combustion engine. Such linear Hall Effect devices are known. Various magnet elements have been used to operate the Hall Effect device to indicate position; however, they usually involve a single magnetic pole which has a non-linear relationship of flux density to distance. When two poles of like polarity have been suggested (SAE Technical Paper Series No. 810379, February, 1981) only linear position is monitored. This is general background to the present invention.